River, Floodplain & Culvert Hydraulics Study

Focused expertise, one engineer, every project.

Land & Watersheds is, admittedly, a one-person operation, but what I lack in staff meetings, I more than make up for in focused expertise and personal attention to every project.

As a water resources engineer, I specialize in hydrologic and hydraulic analysis, drainage design, stormwater management, watershed assessment, and site-improvement design. I work with residential property owners, developers, and municipalities across Puerto Rico to solve complex drainage problems, design site improvements that work with natural hydrology, assess environmental impacts, and ensure regulatory compliance.

My approach combines rigorous technical analysis with practical, site-specific solutions that actually work in the field, not just on paper. Whether you are dealing with unexpected flooding, erosion issues, grading and drainage plans for your development, or permitting challenges, Land & Watersheds provides the specialized knowledge and dedicated service that only comes from working directly with the engineer handling your case. No hand-offs, no miscommunication, just straightforward expertise when you need it most.

David Vagnetti

Civil Site & Water Resources Engineer

David believes in free enterprise and individual responsibility, which is why he left the corporate world to build Land & Watersheds. He prides himself on personal service and an artistic eye, and enjoys helping clients in flood-prone areas realize that, in many cases, “it does not have to be that way.”

Selected river, culvert & scour projects.

This list is by no means exhaustive; many more available upon request.

Project understanding.

We are pleased to submit this proposal to conduct the riverine hydrologic and hydraulic (H&H) study for [Project Name] along [River / Quebrada] at [PR-000 at Km 0.0], [Barrio / Municipality], Puerto Rico.

The study develops design discharges for the contributing watershed, establishes or refines the Base Flood Elevations (BFE) at the crossing, models the river reach and the [culvert / bridge / channel] hydraulics in two dimensions, and designs the scour countermeasures needed to protect the embankment and structure.

Site conditions

The site lies along [River / Quebrada] within [FEMA Zone AE / A] of the effective FIRM. The existing crossing is a [size / type] structure with documented [scour / overtopping] concerns. Available data include the effective Flood Insurance Study, NOAA Atlas 14 rainfall, USGS gage records, and best-available LiDAR; channel cross-sections and the structure invert are confirmed by survey.

Scope of services.

A · Site & data review

• Review of the effective FEMA Flood Insurance Study (FIS), FIRM panels, and any advisory or preliminary Base Flood Elevations for the reach.
• Compilation of NOAA Atlas 14, Volume III rainfall depth-duration-frequency data for the watershed.
• Compilation of USGS stream-gage records and StreamStats regional-regression estimates for verification.
• Assembly of best-available LiDAR / topography and survey of channel cross-sections and structure geometry.

B · Watershed hydrology (GEOHEC-HMS)

• Delineate the contributing basin and sub-basins; assign loss (CN), transform (unit hydrograph), and channel-routing parameters.
• Develop design-storm hydrographs for the 2-, 5-, 10-, 25-, 50-, 100- (and 500-) year events using NOAA Atlas 14 rainfall.
• Verify peak discharges against USGS gage / regression estimates and tabulate design flows at the crossing.

C · River & structure hydraulics (GEOHEC-RAS 2D)

• Build a 2D terrain mesh of the channel and floodplain with land-cover-based roughness and appropriate boundary conditions.
• Compute water-surface elevations, depths, and velocities; establish or refine the Base Flood Elevations through the reach.
• Model the [culvert / bridge] crossing under inlet and outlet control; report headwater, capacity, and overtopping for each event.

D · Scour analysis & countermeasures

• Compute contraction and local (pier / abutment) scour per FHWA HEC-18; evaluate channel stability.
• Size riprap apron, cutoff walls, and wingwall / embankment protection per HEC-23 and HEC-11.
• Provide a stable-channel check and, if required, the basis for a No-Rise / No-Impact certification.

Methodology & data sources.

Information required from the Owner

All hydrologic and regulatory inputs (rainfall, gage data, FIS/FIRM, and terrain) are developed by us. The only items required from the Owner to finalize the analysis are the survey items at the crossing:

• Topographic survey of the channel cross-sections and the structure invert / soffit elevations.
• As-built or record drawings of the existing [culvert / bridge] crossing, where available.

Accurate channel and structure geometry control the computed water-surface and scour, and must be established before the hydraulics can be finalized.

Deliverables.

• Signed and sealed Hydrologic & Hydraulic Report covering methodology, input data, model results, and conclusions.
• Design discharges (GEOHEC-HMS) for each return period at the crossing.
• Water-surface / Base Flood Elevation profiles and 2D depth & velocity maps through the reach.
• Culvert / bridge capacity, headwater, and overtopping analysis for each event.
• Scour computations and riprap / countermeasure design (apron, cutoff walls, wingwalls).
• Supporting figures (effective FIRM, BFE, basin, 2D mesh) and electronic model files (GEOHEC-HMS & GEOHEC-RAS 2D).

Assumptions, exclusions & client-provided information.

This scope assumes access to existing survey/as-builts, right-of-entry for limited site reconnaissance if desired, and availability of best-available topography. Excluded (can be added by amendment): new topographic survey, subsurface investigations, geotechnical design, environmental permitting, and final construction documents.

Calibration beyond reasonableness checks is excluded; if requested, we can develop a calibration plan using nearby USGS gages or high-water-mark data. Freeboard and roadway-serviceability criteria follow local ordinance / owner preference and applicable PRDNER and FEMA standards. A formal FEMA No-Rise certification, CLOMR / LOMR submittal, or sediment-transport study can be added as optional tasks.

Fee summary.

Proposal excludes survey costs and assumes schematic (not-for-construction) designs. Valid for 30 days after submission.

Schedule & timeline.

Terms & conditions.

• Unless amended in writing, the contents of this proposal supersede any plans or verbal discussions.
• Materials, equipment, and methods specified will at all times meet or exceed building codes.
• Land & Watersheds is not responsible for deficiencies, errors, or omissions that are a direct result of the survey data or geotechnical report.
• Land & Watersheds will provide the services outlined in this proposal.

Acceptance & sign-off.

Land & Watersheds proposes the services outlined herein for an all-inclusive fee of [$7,280.00]. Additional charges will be incurred if the project scope changes after this document is signed. The next step is to agree to this proposal (with any noted changes) and sign the contractual agreement that references it.

Land & Watersheds · Water Resources Engineering · Puerto Rico · [email] · [phone]